Recently, there has been performed development of a small-sized light source device utilizing laser Compton scattering. Strength of such a light source device as a light source depends on strength of a realizable laser target. In a case of being based on pulse-driven linear accelerator, laser light is adopted with a method to use high-strength pulse laser or to be used as being temporally burst-amplified.
In contrast, in a case to increase mean strength of laser with a continuously-operated system based on an accumulation ring type apparatus and a superconducting accelerator utilizing Compton scattering, high-strength laser targets are continuously required.
In a traditional X-ray generating device (e.g., see Patent Literature 1) which generates an X-ray with laser inverse Compton scattering at collision between laser light and electrons, strong laser light is generated using a laser generating device which includes a known high-strength mode-locking oscillator (e.g., high-strength mode-locking oscillator having performance of 500 W, 10 psec/pulse, wavelength of 1064 nm, and a repetition frequency of 150 MHz) and an optical accumulation resonator.
Here, the optical accumulation resonator denotes an optical resonator which confines laser light in a space formed by closing an optical path with a plurality of mirrors. This is a promising technology with which high-strength laser light can be continuously actualized as effectively strengthening light from a relatively low-power laser light source.
FIG. 22 illustrates a structural example of a traditional laser accumulation apparatus. Output from a laser resonator is accumulated in an external resonator which is separately prepared. For accumulating light in the optical resonator, it is required to satisfy conditions under that a steady wave is generated in the optical resonator, that is, that a distance between mirrors is matched with an integral multiple of a half wavelength. A resonance width thereof is determined by a reflection rate of resonator mirrors and becomes narrow with usage of mirrors having a high reflection rate for obtaining a higher increase rate. With a resonator having an increase rate of 1000, the resonance width becomes on the order of subnanometers in positional accuracy of the resonance mirrors, so that a resonance state is easily destroyed with environmental disturbance such as vibration. Here, in order to maintain a laser accumulation state as mechanically controlling resonance conditions, it is required to perform advanced feedback control with piezoelectric driving of the resonance mirrors. Presently, technical limitations for maintaining stable resonance stay with the increase rate on the order of 1000.